What is Nebadon?

Does Nebadon consist of the Milky Way galaxy or our entire observable universe? Does the term "local universe" refer to our entire universe, with other universes parallel to it, or does it refer to our galaxy, our local part of the universe?

We are not human beings having a spiritual experience; we are spiritual beings having a human experience. -
Teilhard de Chardin

In the language of faintly glimpsed relativistic quantum dynamics, native science does not yet allow for seven Master Spirits to collapse their wavefunctions of all possible universes into seven discrete, explicit, transcendental realities. This is just one of many factors that will need to be accommodated in a future description of the splendid material reality centered on the material Source and Center.

Native progress wrt evolving a bigger big picture will take a while. But this is "by design".

Does Nebadon consist of the Milky Way galaxy or our entire observable universe? Does the term "local universe" refer to our entire universe, with other universes parallel to it, or does it refer to our galaxy, our local part of the universe?

The whole superuniverse of Orvonton has a radius of only about 250,000 light years and Nebadon itself is only a relatively small patch of Orvonton, 1/100,000 of it (as Rick also points out). Nebadon is just a tiny part of the Milky Way galaxy, it isn't near to being on the scale of a whole galaxy itself, much less the observable universe.

Paper 32, section 2: "The Satania system of inhabited worlds is far removed from Uversa and that great sun cluster which functions as the physical or astronomic center of the seventh superuniverse. From Jerusem, the headquarters of Satania, it is over two hundred thousand light-years to the physical center of the superuniverse of Orvonton, far, far away in the dense diameter of the Milky Way. Satania is on the periphery of the local universe, and Nebadon is now well out towards the edge of Orvonton. From the outermost system of inhabited worlds to the center of the superuniverse is a trifle less than two hundred and fifty thousand light-years."

What this passage is getting across is that within the whole superuniverse of Orvonton, the part that is "Nebadon" is situated "well out towards the edge" in the superuniverse. Within a local universe like Nebadon are further administrative subdivisions, and down on the "system" level, the particular system that contains our world (called Satania) is itself on the periphery of Nebadon. The distance of our system HQ to the superuniverse HQ is 200,000 light years, which puts us among the more distant of inhabited worlds and relatively on the outskirts of Orvonton. The most distant inhabited worlds in Orvonton from the Orvonton HQ are almost 250,000 light years from it. We're considered to be among those who are really far from the center of Orvonton, the capital Uversa, but on the scale of galaxies and the cosmos as whole, it's a pretty piddling distance. Superuniverses are not that big compared to the master universe as a whole.

Good Question, Howard509! This issue is even more interesting than imagined by native speculators. See: (1318.5) 119:8.6 -- after Michael earned his rulership of Nebadon, his more-than-finite attributes were truly verified, earning him personal involvement in activities of the "Trinity of Ultimacy".

Also, any concept of Nebadon (c.f. the larger creative units) must allow for the space-time independence [(377.2) 34:3.6] of our local universe parents. Especially interesting is Michael's independence of time:

"If the transactions of the evolutionary worlds are excepted, these Michael Sons seem to be able to operate relatively independent of time. A Creator Son is not handicapped by time, but he is conditioned by space;" (377.1) 34:3.5

Does this mean our Michael is currently (i.e. now) able to act at any time in the evolution of Nebadon? Does this mean he can adjust both the beginnings and endings of Nebadon simultaneously? This would make sense of all those restrictions placed upon (and agreed to by) Master Michaels! And consider his "better half" -- she can act ubiquitously, i.e. at any and all places throughout Nebadon, at some given moment of time:

"The Divine Minister is the understanding helper of the Creator Son, enabling him to overcome and atone for his inherent limitations regarding space, for when these two function in administrative union, they are practically independent of time and space within the confines of their local creation. Therefore, as practically observed throughout a local universe, the Creator Son and the Creative Spirit usually function independently of both time and space since there is always available to each the time and the space liberation of the other." (377.2) 34:3.6

Regarding popular notions of multiverses and parallel universes, these mostly stem from the quip, "anything that can happen will happen." Feynman fostered this belief with his cute but crude device of path integrals ("the wav~icle takes all possible paths").

Don't forget that our adjuster and person-ness are both rooted in Dad's absolute domain, so with regard to adjusted persons, what happens when and where is by definition very ill-defined. As I mentioned above, native science does not yet allow for a global observer "to collapse the wave function". The UB reveals many levels of finite and more-than-finite guidance to keep the reified universe on track.